What is an Atom Definition

An atom is the most discrete indivisible particle that forms an element. Atoms of the same element are identical; different elements have non-similar atoms. The most simple of all elements is Hydrogen. 
Example: Hydrogen atoms are similar while Oxygen atoms are different than Hydrogen atoms. Two hydrogen atoms and one Oxygen combined form the water molecule H2O.

The atoms are extremely small. Therefore, even the most powerful microscopes cannot see them. Actually, 6.022X10^23 hydrogen atoms (Avogadro Number) weigh only one gram. There are 454 grams in one pound.

In order to understand the nature of the atom, we should identify the forces that are holding it together. Much as our plant, gravity is the force holding the moon in its orbit around the earth. Gravity is the force of attraction between two large masses.
In the case of the atom, the small size of the particles and the speed at which the electron travels would prohibit a force such as gravity from being able to hold the atom together. Scientists have learned that electrostatic force is the force that maintains the atom.

Atoms Composition

While atoms are composed of small subatomic particles; these particles are the electron, the proton and the neutron. The proton and neutron are found in the nucleus which is the center of the atom. The electron is negatively charged and orbits around the nucleus.

atom composed of subatomic particles electron proton neutron

Atoms from different elements are constituted of the same type of subatomic particles. However, the proportions of the subatomic particles are different for each element. Hydrogen for example has two subatomic particles; an electron and a proton. In the case of hydrogen, a single electron orbits a single proton. ِAn example is the moon which orbits the earth. Same as in the case of earth, the proton of the hydrogen atom is much larger than the electron.

an electron orbits proton in nucleus in an atom like moon orbits earth

Moreover, if we add a subatomic particle to a Hydrogen atom, we create another atom of another element. Note: The number of subatomic particles is what characterizes atoms of different elements. In addition, if we want to create a Helium atom, we should only add an additional electron, an additional proton and two neutrons to the Hydrogen atom. As a result, we’ll have two electrons orbiting four other particles, two protons and two neutrons in the nucleus.